Problem: Kevin is 4 times as old as William and is also 24 years older than William. How old is Kevin?
Explanation: We can use the given information to write down two equations that describe the ages of Kevin and William. Let Kevin's current age be $k$ and William's current age be $w$ $k = 4w$ $k = w + 24$ Now we have two independent equations, and we can solve for our two unknowns. One way to solve for $k$ is to solve the second equation for $w$ and substitute that value into the first equation. Solving our second equation for $w$ , we get: $w = k - 24$ . Substituting this into our first equation, we get the equation: $k = 4$ $(k - 24)$ which combines the information about $k$ from both of our original equations. Simplifying the right side of this equation, we get: $k = 4k - 96$ Solving for $k$ , we get: $3 k = 96$ $k = 32$.